Circuit arrangement and manufacturing method thereof

ABSTRACT

Exemplary embodiments of the disclosure are directed to a circuit arrangement in which a power functional device and a conductor element are mounted and a method of manufacturing the same. The arrangement includes a substrate, a wiring layer provided on the substrate and electrically connected to the functional device and to the conductor element and an intermediate electric contact device. The intermediate electric contact device is mounted on the wiring layer to provide on the side opposite to the wiring layer a contact region for contacting the conductor element. The conductor element is contacting the intermediate electric contact device in the contact region which is opposite to an area, in which the electric contact device is fixed to the wiring layer.

RELATED APPLICATION(S)

This application claims priority as a continuation application under 35U.S.C. §120 to PCT/EP2010/064377, which was filed as an InternationalApplication on Sep. 28, 2010 designating the U.S., and which claimspriority to European Patent Application No. 09171447.7 filed in Europeon Sep. 28, 2009, the entire contents of which are hereby incorporatedby reference in their entireties.

FIELD

The disclosure relates to a semiconductor mount, such as a circuitarrangement in which a power functional device, such as a transistor ordiode, and a conductor element are mounted.

BACKGROUND INFORMATION

Document EP 1 711 040 B1 describes a circuit device in which afunctional device and an externally leading conductor are mounted, thecircuit device including a substrate, a wiring layer provided on thesubstrate and electrically connected to the functional device and to theexternally leading conductor, and an additional coating metal layerformed on a part of the wiring layer to provide a corresponding contactregion for contacting the functional device. The wiring layer and theadditional coating metal layer constitute a metallization of thesubstrate. Low temperature bonding specifies silver plating which canhinder the use of ultra sonic welding for the terminals.

The metallization constituted by the wiring layer and the coating metallayer on the part of the wiring layer contributes with relatively highresistivity contribution (about 30μΩ) to the overall arrangementresistance. One possible solution is using a substrate metallizationthat is in general thicker for decreasing the resistivity. A problemwhen increasing the metallization thickness is that the layouttolerances increase at the same time. Therefore, the layout would haveto be changed with loss of cross sectional area again.

Another drawback of a generally thicker substrate metallization is thatthe mechanical stresses at the metallization edges of the wiring layerwill increase where crack growth in the ceramic substrate is initiated(the polyimide might prevent it).

From EP 1 830 406 A1 a power module is known, which includes a powersemiconductor mounted on top of a heat spreader. As shown in the figuresof EP 1 830 406 A1 the heat spreader is aligned with the element onwhich it is mounted.

From DE 43 00 516 A1 another power module is known. In this known powermodule, a contact plate is arranged on top of a diode in order to easethe connection to a massive copper element.

From “Low-inductance module construction for high speed, high-currentIGBT module suitable for electric vehicle application” by T. Tsunoda etal. (Power Semiconductor devices and ICS, 1993, ISPSD '93., Proceedingsof the 5th International Symposium on Monterey, Calif., USA 18-20 May1993, New York, N.Y., USA IEEE, US, 18 May 1993) a multi-layered DBCsubstrate is known. By the proposed construction, the collector andemitter terminals are arranged closely to each other in order tocompensate for the magnetic field generated by the current flow inindividual terminals.

SUMMARY

An exemplary circuit arrangement is disclosed comprising: a substrate; awiring layer provided on the substrate and electrically connected to apower functional device and to a conductor element; and an intermediatecontact device, which is mounted on the wiring layer to provide acontact region for contacting the conductor element on a side oppositeto the wiring layer, wherein the intermediate contact device has atleast a first side and a second side, the second side is at leastsubstantially parallel to the first side, wherein the intermediatecontact device is fixed to the wiring layer on the first side, whereinthe conductor element is contacting the intermediate contact device onthe second side in the contact region

An exemplary method of manufacturing a circuit arrangement is disclosed,in which at least one power functional device and at least one conductorelement is mounted, wherein the arrangement includes a substrate and awiring layer provided on the substrate, the method comprising the stepsof: mounting and electrically contacting an intermediate contact deviceon the wiring layer to provide a contact region on one side of theintermediate contact device, which is opposite to the wiring layer; anddirectly electrically connecting the conductor element to theintermediate contact device in the contact region.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the disclosure will be apparent from andelucidated with reference to the embodiments described hereinafter.

In the drawings:

FIG. 1 depicts a first circuit arrangement in accordance with anexemplary embodiment of the present disclosure;

FIG. 2 shows a sectional view of the first circuit arrangement inaccordance with an exemplary embodiment of the present disclosure;

FIG. 3 shows a circuit arrangement in accordance with an exemplaryembodiment of the present disclosure;

FIG. 4 shows a sectional view of a third circuit arrangement inaccordance with an exemplary embodiment of the present disclosure; and

FIG. 5 shows a fourth circuit arrangement in accordance with anexemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

Exemplary embodiments of the present disclosure provide a circuitarrangement, which overcomes the aforementioned disadvantages.

An exemplary intermediate electric contact device is fixed to theaccording part of the wiring layer only in finite sub-areas of theentire outer side (or interface) of the wiring layer. The intermediatecontact device has a first side on which the intermediate contact deviceis fixed to the wiring layer. Opposite to the part of the wiring layer,in which the intermediate contact device is fixed to the wiring layer,the intermediate contact device has a contact region, in which theconductor element is contacting the intermediate contact device. By thisarrangement, the wiring layer as well as the substrate can be protectedfrom damages during attaching of the conductor element.

An advantage provided by the exemplary embodiments described herein caninclude when fixing the intermediate contact device on top of a track ofthe wiring layer which is thinner than the intermediate contact device,the stress at the metallization edge at the wiring layer is notincreased much because a fixation area of the fixation is smaller thanthe metallization area below. There is a margin between the intermediatecontact device and the metallization edge.

According to an exemplary embodiment of the present disclosure, theintermediate contact device is fixed to the wiring layer by solderingand/or low-temperature bonding (LTB).

According to another exemplary embodiment of the present disclosure, theconductor element is an externally leading conductor.

According to yet another exemplary embodiment of the present disclosure,the power functional device is a power transistor, such as an insulatedgate bipolar transistor, or a (power) diode. The insulated gate bipolartransistor or IGBT is a three-terminal power semiconductor device, notedfor high efficiency and fast switching. In the active state of the IGBT,a voltage or potential difference between the emitter as well as acorresponding emitter track and the gate as well as the correspondinggate track of the IGBT is a low voltage. Furthermore, selectivelythickening the emitter tracks is less critical for reliability becausethe emitter track does not see higher temperatures than the collectortracks.

According to one exemplary embodiment of present disclosure, the atleast partial electrically conductible contact device is a metal foil ormetal plate. The metal plate can be standard insulated metal technology(IMS). The bonding of the plate can be done in the process step as thebonding of the power functional device (die-bonding). The metal foil ormetal plate can be thicker than 100 μm or 200 μm, for example.

According to another exemplary embodiment of the present disclosure, theat least partial electrically conductible contact device is a circuitboard for selectively contacting other elements and/or devices of thecircuit arrangement.

According to yet another exemplary embodiment of the present disclosure,the intermediate contact device and at least one bonding element forelectrically contacting the power functional device with the wiringlayer are integrally formed. The intermediate contact device beingintegrally formed with the bonding element saves costs and simplifiesthe mounting of the arrangement.

Exemplary embodiments of the present disclosure further relate to amethod of manufacturing a circuit arrangement in which at least onefunctional device and at least one conductor element is mounted, whereinthe arrangement includes (e.g., comprises) a substrate and a wiringlayer provided on the substrate, the method including the steps ofmounting and electrically contacting an intermediate contact device onan the wiring layer to provide contact region on one side of theintermediate contact device, which is opposite to the wiring layer (14),and directly electrically connecting the conductor element to theintermediate contact device in the contact region.

According to an exemplary embodiment of the present disclosure, theintermediate contact device is fixed to the wiring layer by solderingand/or low-temperature bonding (LTB).

According to another exemplary embodiment of the present disclosure, thewiring device is an externally leading conductor or terminal of thearrangement.

According to yet another exemplary embodiment of the present disclosure,the power functional device is a power transistor, such as an insulatedgate bipolar transistor, or diode.

According to one exemplary embodiment of the present disclosure, the atleast partial electrically conductible contact device is a metal foil ormetal plate. The metal plate can be standard IMS technology. The bondingof the plate can be done in the process step as the bonding of the powerfunctional device (die-bonding). The metal foil or metal plate can bethicker than 100 μm or 200 μm, for example.

According to another exemplary embodiment of the present disclosure, theat least partial electrically conductible contact device is a circuitboard.

According to yet another exemplary embodiment of the present disclosure,the intermediate contact device and at least one bonding element forelectrically contacting the power functional device with the wiringlayer are integrally formed. The intermediate contact device beingintegrally formed with the bonding element saves costs and simplifiesthe mounting of the arrangement.

FIG. 1 depicts a first circuit arrangement in accordance with anexemplary embodiment of the present disclosure; and FIG. 2 shows asectional view of the first circuit arrangement in accordance with anexemplary embodiment of the present disclosure.

Together FIGS. 1 and 2 show a power circuit arrangement 10 including asubstrate 12 being a ceramic substrate and a structured wiring layer 14provided on the substrate 12. The wiring layer 14 has at least a firsttrack and a second track, which is insulated from the first track. In anexemplary embodiment, the first track can be formed by a collector track36 and the second track can be formed by an emitter track 30. The wiringlayer could also be formed to have more than two tracks as desired. Thewiring layer 14 can have a third track formed as a gate track. Thestructured wiring layer 14 can be made of copper. The wiring layer 14can have a thickness of 200 μm to 400 μm. In the exemplary circuitarrangement 10 of the present embodiment, six power functional devices16 (not shown in detail), and a plurality of conductor elements 18 aremounted on the power circuit arrangement 10. The power functionaldevices 16 are power semiconductor devices such as power transistors 20,for example, power IGBTs (IGBT: Insulated Gate Bipolar Transistor), anddiodes. The conductor elements 18 can include externally leadingconductors 22 for externally connecting the power functional device 16outside the circuit arrangement 10 and/or bonding elements, inparticular bonding wires 25. The externally leading conductors 22 caninclude L-shaped power terminals of the circuit arrangement. These powerterminals can be formed of so called “moly plates”, such as a metal-freecompound composed of molybdenum disulfide and graphite, which caninclude a synthetic non-melting carrier.

As shown in FIG. 1, the power circuit arrangement 10 has four externallyleading conductors 22. Between each of the externally leading conductor22 and the respective area of the wiring layer 14 just below theexternally leading conductor 22 an intermediate contact device 26 isarranged. The intermediate contact device 26 has a first side and asecond side which is at least approximately parallel to the first side.The first side of the intermediate contact device 26 is electricalconductively fixed to the wiring layer 14. On the second side, theintermediate contact device 26 provides a contact region for contactingat least one conductor element 18, for example the externally leadingconductor 22. The conductor element 18 is electrical conductively fixedon the intermediate contact device 26. Further, the contact region isopposite of the area on the first side in which the intermediate contactdevice is electrical conductively fixed to the wiring layer 14.

The intermediate contact devices 26 between the conductor elements 18,e.g. the externally leading conductors (terminals) 22, and the wiringlayer 14 protect the ceramic substrate 12 when bonding the externallyleading conductors 22 by ultrasonic welding (also laser and resistivewelding). For that purpose the intermediate contact devices 26 shouldalso be bonded on top of the parts of the structured wiring layer 14being the collector tracks 36, emitter track 30 and/or the gate track28′ just below the feet of the externally leading conductors 22(terminal feet). It should be understood, that the intermediate contactdevice 26 should be used if connecting the conductor element 18 directlyto the wiring layer 14 could damage the ceramic substrate 12 and/or thewiring layer 14. Thus in other exemplary embodiments one or several ofthe conductor elements 18, in particular one or several of theexternally leading conductors 22 can be connected to the respectivetrack of the wiring layer by an intermediate contact device 26.

The intermediate contact device can be formed of a metal foil or metalplate. Hence, the intermediate contact device 26 is self-contained. Thebonding of the metal foil or metal plate can be done in the process stepas the bonding of the power functional device (die-bonding). The metalfoil or metal plate can be thicker than 100 μm or 200 μm, for example.

In general, the power functional devices 16 can be electricallyconnected to the externally leading conductors 22 via their connectorareas (not shown), bonding elements being bonding wires 25 and theintermediate contact devices 26 as well as tracks 36 established by thewiring layer 14 and intermediate contact devices 26.

In the exemplary embodiment shown in FIGS. 1 and 2, an upper or emittercontact of each of the power functional devices 16 is electricallycontacted by bonding wires 25 leading to a metal foil 34 arranged on theemitter track 30 of the wiring layer 14. The metal foil 34 can be anexemplary embodiment of the intermediate contact device 26 according tothe present disclosure. A lower or collector contact of each of thepower functional devices 16 is in electrical contact to one of thecollector tracks 36 of the wiring layer 14. Further, on each collectortrack 36 a metal plate 38 is arranged, which is a further embodiment ofthe intermediate contact device 26. As described above, the metal plate38 on the collector tracks 36 is for protecting the ceramic substrate12. The metal foil 34 on the emitter track 30 is not only for protectingthe ceramic substrate 12 but also for lowering the resistivity asdiscussed below.

The intermediate contact devices 26 can be arranged in direct electricalcontact to the conductor elements 18 (for example the externally leadingconductors 22) and/or to the wiring layer, which can be formed by the atleast first and second track, in particular the collector track 36 andthe emitter track 30 for the IGBT transistors 20.

An additional electrical resistance film 32 is located between the gatetrack 28 formed by an additional wiring strip and the emitter track 30formed by the respective part of the structured wiring layer 14 and theintermediate contact device 26 being a metal foil 34. The metal foil 34is electrical conductively fixed on the respective part of thestructured wiring layer 14. The gate track 28 and the intermediatecontact device, on which the gate track 28 is provided, can be formed bya partial electrically conductible metal foil or metal plate byinsulated metal technology (IMS).

Each of the two collector tracks shown in FIGS. 1 to 5 directly contactsthree IGBTs and/or diodes by their collector connector areas.

According to an exemplary embodiment of the present disclosure, theintermediate electric contact devices 26 are mounted on a respectivepart of the wiring layer 14 to provide a corresponding contact regionfor contacting the power functional device 16. Further, an intermediateelectric contact device 26 is mounted on one part of the wiring layer 14that forms the emitter track 30.

As shown in more detail in FIG. 2, in the circuit arrangement 10 can bea metallic plate or thick metallic foil 34 is bonded on the part of thewiring layer 14 building the emitter track 30. The plate or foil 34provides on top the additional metallization or wiring strip being thegate track 28 for the IGBTs. The plate or foil can be standard IMStechnology (“DENKA HITT PLATE”). The bonding of the plate or foil 34 canbe done in the process step as the bonding of the power functionaldevices 16 (being a die-bonding). The bonding method can includesoldering or low-temperature bonding (LTB). Thus, the joint between thewiring layer 14 and the intermediate contact device 26 is a solderingjoint or a joint made by low-temperature bonding. The plate on top ofthe part of the wiring layer 14 lowers the resistance of the overallemitter path. For a standard IGBT module (e.g. “HiPak2”) the reductioncould be more than 10μΩ. For a 1700 V/3600 A arrangement or module, thisreduces the voltage drop by more than 36 mV (around 1.5% of the on-statvoltage).

The gained thickness of the emitter track 30 allows making the emittertrack 30 narrower. The narrower emitter track 30 allows to reduce theoverall area of the substrate 12 or to form a larger area of thecollector tracks 36. A corresponding arrangement is shown in FIG. 3.

FIG. 3 shows a circuit arrangement in accordance with an exemplaryembodiment of the present disclosure. FIG. 3 is a variant of theembodiment shown in FIG. 2, wherein the width of the emitter track 30 isnarrower than in the embodiment of the circuit arrangement 10 shown inFIG. 2. The larger area of the collector track 36 increases the heatspreading. Having a larger distance between the surface of the substrate12 and the heating power functional device 16 will also improve the casetemperature cycling capability because there is less temperaturedifference ΔT and thus less stress at the surface of the substratesolder.

Because of the narrower emitter track 30, larger collector tracks 36 canbe used with a substrate 12 of the same size. FIG. 4 shows a sectionalview of a third circuit arrangement in accordance with an exemplaryembodiment of the present disclosure. FIG. 4 shows an according circuitarrangement with larger collector tracks. The active area of thecollector tracks can be increased by more than 10%.

FIG. 5 shows a fourth circuit arrangement in accordance with anexemplary embodiment of the present disclosure. FIG. 5 is a variant ofthe exemplary embodiments shown in FIGS. 1 to 4, wherein a plurality ofbonding metal sheets 38 electrically connecting the emitter track 30 tothe corresponding emitter connector areas of the power functionaldevices 16 and the intermediate contact device 26 connecting the emittertrack 30 with the corresponding (emitter) conductor element 18 being anexternally leading conductor 22 are integrally formed as a intermediatecontact device 26 fixed to the emitter connector area of the powerfunctional devices 16 and to the corresponding (emitter) conductorelement 18. This intermediate contact device 26 shown in FIG. 5 isdirectly contacting the emitter of the power functional device 16 and/orthe corresponding conductor element 18.

In the die-attach process intermediate contact devices 26, such as metalplates 38, can be bonded that provide several functions. Lowering theelectric resistance, protection of the ceramics when welding the powerterminals (e.g. strong moly plates), and carrying the gate circuit ontop.

The corresponding exemplary manufacturing method includes the steps offixing the intermediate contact device, e.g. the metal foil 34 or plate38, on an according part of the wiring layer 14 only in finite sub-areasof the entire outer side of the wiring layer to provide a correspondingcontact region for the conductor element 18, and directly or indirectlyelectrically connecting the functional device(s) and the conductor 22 tothe metal foil 34 or plate 38.

The corresponding resistance of the collector tracks drops from 8.2μΩ into 6.8μΩ, the resistance of the emitter track drops from 24.2μΩ in to6.8μΩ, the total reduction is about 18.8μΩ.

In further exemplary embodiments, only one or several of theintermediate contact devices shown in FIGS. 1 to 5 can be arranged onthe wiring layer 14. It is also possible that at least one conductorelement 18 can be directly connected to the wiring layer 14.

While the disclosure has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive; thedisclosure is not limited to the disclosed embodiments.

Other variations to be disclosed embodiments can be understood andeffected by those skilled in the art in practicing the claimeddisclosure, from a study of the drawings, the disclosure, and theappended claims. In the claims, the word “comprising” does not excludeother elements or steps, and the indefinite article “a” or “an” does notexclude a plurality. The mere fact that certain measures are recited inmutually different dependent claims does not indicate that a combinationof these measures cannot be used to advantage. Any reference signs inthe claims should not be construed as limiting scope.

Thus, it will be appreciated by those skilled in the art that thepresent invention can be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Thepresently disclosed embodiments are therefore considered in all respectsto be illustrative and not restricted. The scope of the invention isindicated by the appended claims rather than the foregoing descriptionand all changes that come within the meaning and range and equivalencethereof are intended to be embraced therein.

REFERENCE SIGNS LIST

-   10 circuit arrangement-   12 substrate-   14 wiring layer-   16 functional device-   18 conductor element-   20 power transistor-   22 externally leading conductor-   24 bonding wire-   25 bonding metal sheet-   26 intermediate contact device-   28 gate track-   30 emitter track-   32 resistance film-   34 metal foil-   26 collector track-   38 metal plate

1. A circuit arrangement comprising: a substrate; a wiring layerprovided on the substrate and electrically connected to a powerfunctional device and to a conductor element; and an intermediatecontact device, which is mounted on the wiring layer to provide acontact region for contacting the conductor element on a side oppositeto the wiring layer, wherein the intermediate contact device has atleast a first side and a second side, the second side is at leastsubstantially parallel to the first side, wherein the intermediatecontact device is fixed to the wiring layer on the first side, whereinthe conductor element is contacting the intermediate contact device onthe second side in the contact region.
 2. The circuit arrangementaccording to claim 1, wherein the intermediate contact device is fixedto the wiring layer by at least one of a soldering joint and by a jointmade by low-temperature bonding.
 3. The circuit arrangement according toclaim 1, wherein the intermediate electric contact device is fixed to apart of the wiring layer in finite sub areas of an entire outer side ofthe wiring layer.
 4. The circuit arrangement according to claim 1,wherein the conductor element is an externally leading conductor or abonding element leading from the intermediate contact device to thepower functional device.
 5. The circuit arrangement according to one ofclaim 1, wherein the power functional device is a power semiconductordevice.
 6. The circuit arrangement according to claim 1, wherein theintermediate contact device is at least partially electricallyconductible, and wherein the intermediate contact device is one of ametal foil, a metal sheet or a metal plate.
 7. The circuit arrangementaccording to claim 1, wherein the at least partially electricallyconductible intermediate contact device is a circuit board.
 8. Thecircuit arrangement according to claim 1, wherein the intermediatecontact device is thicker than 100 μm.
 9. The circuit arrangementaccording to claim 1, wherein the intermediate contact device and abonding element for electrically contacting the power functional devicewith the wiring layer are integrally formed.
 10. The circuit arrangementaccording to claim 1, wherein the intermediate contact device is indirect electrical and mechanical contact to the wiring layer.
 11. Thecircuit arrangement according to claim 1, wherein the intermediatecontact device is self-contained.
 12. The circuit arrangement accordingto claim 1, wherein the contact region is opposite to an area on thefirst side in which the intermediate contact device is electricallyconductively fixed to the wiring layer.
 13. The circuit arrangementaccording to claim 15, wherein the power semiconductor device is a powertransistor including one of an insulated gate bipolar transistor and adiode.
 14. A method of manufacturing a circuit arrangement, according toclaim 1, in which at least one power functional device and at least oneconductor element is mounted, wherein the arrangement includes asubstrate and a wiring layer provided on the substrate, the methodcomprising the steps of: mounting and electrically contacting anintermediate contact device on the wiring layer to provide a contactregion on one side of the intermediate contact device, which is oppositeto the wiring layer; and directly electrically connecting the conductorelement to the intermediate contact device in the contact region. 15.The method according to claim 14, wherein mounting the intermediatecontact element to a part of the wiring layer includes fixing theintermediate contact element to the part only in finite sub-areas of theentire outer side of the wiring layer.
 16. The method according to claim14, wherein the intermediate contact device is fixed to the wiring layerby soldering and/or low-temperature bonding.
 17. The method according toclaim 14, wherein the conductor element is an externally leadingconductor.
 18. The method according to claim 14, wherein the powerfunctional device is a power semiconductor.
 19. The method according toclaim 14, wherein the intermediate contact device is at least partialelectrically conductible, and wherein the intermediate contact device isone of a metal foil, a metal sheet or a metal plate.
 20. The methodaccording to claim 14, wherein the intermediate contact device is atleast partially electrically conductible, and wherein the intermediatecontact device is a circuit board.
 21. The method according to claim 12,wherein the intermediate contact device and a bonding element forelectrically contacting the power functional device with the wiringlayer are integrally formed.
 22. The method according to claim 18,wherein the power semiconductor is a power transistor including one ofan insulated gate bipolar transistor and a diode.